Experiments aimed at mapping genes and determining the distribution of genetic sequences on the DNA molecules of higher organisms are proposed. The basic technique used is the electron microscope heteroduplex method combined with chemical labeling procedures. The results will provide information on the structural basis of the regulation of gene function. BIBLIOGRAPHIC REFERENCES: Mapping of Poly(A) Sequences in the Electron Microscope Reveals Unusual Structure of Type C Oncornavirus RNA Molecules. Welcome Bender and Norman Davidson. Cell 7, 595-607 (1976). Gene Mapping by Electron Microscopy. Norman Davidson, in "Molecular Biology of the Mammalian Genetic Apparatus" (1976) editor P.O.P. Pso, associated Scientific Publishers, Elsevier Excerpta Medica, North Holland, in press.